Friend leukemia cells grown in the presence of dimethyl sulfoxide (DMSO) and a number of other inducers are stimulated to differentiate along the erythroid line. The mechanisms of action of the inducers, many of which are structurally unrelated, are unknown. A study is being made of the effects they have in common. Since all of the inducers we have so far tested cause single-stranded scission in the DNA of the treated cells, we are characterizing the DNA in DMSO-resistant clones that vary in their response to DMSO. Experiments on in vitro transformation of hematopoietic cells by Friend leukemia virus are being continued.